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The present invention relates to medical devices, and in particular, to balloon catheter devices which employ cryogenic fluids to treat complex three-dimensional surfaces.
Recently, the use of fluids with low operating temperatures, i.e. cryogenic fluids or refrigerants, has begun to be explored in the medical and surgical field. Of particular interest are the potential use of catheter based devices, which employ the flow of cryogenic working fluids therein, to selectively freeze, or xe2x80x9ccold-treatxe2x80x9d, targeted tissues within the body. Catheter based devices are desirable for various medical and surgical applications in that they are relatively non-invasive and allow for precise treatment of localized discrete tissues that are otherwise inaccessible.
A cryogenic device uses the energy transfer derived from thermodynamic changes occurring in the flow of a refrigerant through the device. This energy transfer is then utilized to create a net transfer of heat flow from the target tissue to the device, typically achieved by cooling a portion of the device to very low temperature through conductive and convective heat transfer between the refrigerant and target tissue. The quality and magnitude of heat transfer is regulated by device configuration and control of the refrigerant flow regime within the device.
Structurally, cooling can be achieved through injection of high pressure refrigerant through an orifice. Upon injection from the orifice, the refrigerant undergoes two primary thermodynamic changes: (i) expanding to low pressure and temperature through positive Joule-Thomson throttling, and (ii) undergoing a phase change from liquid to vapor, thereby absorbing heat of vaporization. The resultant flow of low temperature refrigerant through the device acts to absorb heat from the target tissue and thereby cool the tissue to the desired temperature.
Once refrigerant is injected through an orifice, it may be expanded inside of a closed expansion chamber which is positioned proximal to the target tissue. The resulting heat transfer thus occurs across a surface generally defined by the contact area between the medical device and the target tissue, thereby forming xe2x80x9clesionsxe2x80x9d on the target tissue. Such lesions conform to the particular geometry of the portion of the medical device being cooled by the flow of refrigerant therethough. In other words, the size and shape of the tissue treated is analogous to the geometry of the expansion chamber wherein refrigerant is injected in the medical device. Medical devices which employ such refrigerant injection techniques vary as to size and shape. Devices wherein an expandable membrane, similar to an angioplasty balloon, are employed as expansion chambers, have recently been explored. In such a device, refrigerant is supplied through a catheter tube into an expandable balloon coupled to such catheter, wherein the refrigerant acts to both: (i) expand the balloon near the target tissue for the purpose of positioning the balloon, and (ii) cool the target tissue proximal to the balloon to cold-treat adjacent tissue.
The principal drawback to such a technique is that the balloon geometry is generally spherical or ellipsoidal, as the flexible membrane comprising the balloon either expands in a uniform radial direction, or expands to conform to the geometry of the tissue next to which it is positioned. In both cases, the surface geometry of the expanded membrane does not ideally conform to the surface geometry of the tissue to be treated. Most devices can only form either linear, circular, or spherical lesions, while the desired lesion geometry may be highly complex. This is especially true in the case of body ostia, such as the junctions between arteries or veins and chambers of the head and neck, wherein the surface geometry of the tissue to be treated is either conical, cylindrical, or more often, a complex three-dimensional surface, or some combination thereof.
It is therefore desirable to provide a medical device which maximizes the efficiency of cryogenic cold-treatment, by providing a treatment surface area which is well-suited to create lesions which conform to conical, cylindrical, or other complex three-dimensional surfaces. It is further desirable to provide such a medical device, wherein the size, shape, and geometry of the treatment surface is controllable during operation of the device and consequent cooling of tissue adjacent thereto.
The medical device comprises a first expandable support structure transitionable from a first to a second state, and an expandable membrane enveloping the first support structure to define an expansion chamber when the support structure is in the second state.
In a first embodiment of the invention, the device includes an elongate shaft having proximal and distal end portions, the shaft defining an injection lumen, an exhaust lumen, and an inflation lumen therethrough, each lumen having a proximal end portion and distal end portion proximate the proximal and distal end portions of the shaft, respectively. An expandable support structure is coupled to the distal end portion of the shaft, having an inner surface and an outer surface, the inner surface being in fluid communication with the distal end portion of the inflation lumen to define an inflation chamber inside of the membrane. An expandable membrane having an inner surface and an outer surface is disposed around the support structure, the inner surface being in fluid communication with the distal end portions of the injection and exhaust lumens, to define an expansion chamber between the support structure and the expandable membrane. The inflation lumen is coupled to a supply of inflation medium, whereas the injection lumen is coupled to a supply of refrigerant, wherein after the expandable support structure is inflated by the injection of inflation medium therein, refrigerant is injected into the expansion chamber inside of the expandable membrane, to cool the region adjacent to and surrounding the device proximate to the expansion chamber.
In another embodiment of the invention, both the expandable support structure and the expandable membrane are fluidly coupled to the refrigerant injection and exhaust lumens such that refrigerant may flow throughout both the inflation chamber and the expansion chamber. In a particular application of such an embodiment, the expandable support structure may be injected with refrigerant, while the expandable membrane enveloping the support structure may be actively coupled to the exhaust lumen only, such that vacuum conditions exist in the expansion chamber, whereby the expandable membrane effectively serves as a negative apposition device around the expandable support structure.
In another embodiment of the invention, two expandable membranes are disposed on the distal end portion of the catheter shaft, surrounded by a third expandable membrane to define an expansion between the first two membranes that is substantially toroidal or cylindrical when the first two membranes are inflated by the injection of inflation medium therein. Refrigerant is thereafter injected into the expansion chamber to cool regions immediately adjacent to and outside of the third membrane of the device, proximate to the expansion chamber.